A brief description will be given below of an idle mode of a mobile station and a paging group in relation to exemplary embodiments of the present invention.
A broadband wireless access system supports an idle mode to minimize power consumption of a mobile station. Generally, the idle mode is intended to serve as a mechanism to allow an MS to become periodically available for downlink broadcast traffic messaging without requiring the MS to register to any particular base station as the MS moves in a radio link environment populated by multiple base stations.
During the idle mode, the MS need not be handed off while moving between base stations contained in the same paging zone. Therefore, the MS need not transmit uplink information for the handoff procedure, resulting in a reduction in power consumption.
If the MS has not received traffic from a base station for a predetermined time, it may transition to the idle mode to save power. In the idle mode, the mobile station receives a broadcast message (e.g. a paging message) from the BS during an available interval and determines whether to transition to normal mode or to stay in the idle mode. Also, the mobile station may notify a paging controller of its location by location update in the idle mode.
The idle mode may be beneficial to the mobile station (MS) by relieving the mobile station of an active requirement for handover and normal operational requirements. The idle mode restricts the MS's activity to scanning during discrete periods, so that the mobile station conserves power and operation resources.
Additionally, the idle mode may benefit a network and a BS by providing a simple and timely scheme for alerting an MS to pending downlink traffic directed toward the MS and by eliminating an air interface and network handover (HO) traffic from an inactive MS.
Paging is a function of, upon generation of an incoming call in mobile communications, locating a mobile station for which the incoming call is destined (e.g. detecting a base station or a Mobile Switching Center (MSC) to which the mobile station belongs). A plurality of base stations supporting the idle mode may be divided into specified paging groups, covering paging areas.
The paging groups are logical groups. The purpose of these paging groups is to offer a contiguous coverage area in which the MS can be paged on a downlink (DL) if there is traffic targeted thereto. Preferably, the paging groups are large enough for a mobile station to spend most of its time within the same paging group and small enough to render paging overhead reasonable.
FIG. 1 shows exemplary paging groups, each of which includes a plurality of base stations.
FIG. 1 shows four paging groups defined in multiple BSs each located at a hexagonal lattice. One paging group may be included in one or more paging groups.
The paging groups are defined in a management system. A paging group may use a paging group-action backbone message. The paging controller uses another backbone network message (paging-announce message), to manage the list of mobile stations in the idle mode and initiate paging of a mobile station on all base stations belonging to a paging group.
A paging group may include one or more base stations, and one BS may be contained in one or more paging groups. The paging groups may be defined in a management system. A paging group may use a paging group-action backbone network message. In addition, a paging controller uses another backbone message (paging-announce message) in order to manage the list of mobile stations in an idle mode and initiate paging of a mobile station on all base stations belonging to a paging group.
If the mobile station requests that the base station enter the idle mode, the base station transmits its own paging group ID to the mobile station, so that the mobile station can enter the idle mode.
Next, a paging procedure and location update method according to the related art will hereinafter be described in detail.
If a paging controller receives an incoming call or packet for the mobile station that stays in the idle mode, the paging controller transmits a paging message to all base stations contained in each paging group, the base stations each having received the paging message broadcast a paging advertisement message to all mobile stations managed by the base stations. Each mobile station receives the paging advertisement message from the base stations during an available interval, so that they determine whether to enter a normal mode or to stay in the idle mode. In other words, if the paging controller pages the mobile station, the mobile station enters the normal mode so that it can communicate with a serving base station.
If a location update condition is satisfied, the MS in the idle mode updates its location. There are a variety of location update conditions, for example, a paging group location update, a timer based location update, a power down location update, and the like.
The paging group location update condition is as follows. If the mobile station moves out of an area of the paging group to which the mobile station belongs and enters another paging group, the mobile station performs location update. The paging group location update condition means that the mobile station performs location update when a location update timer has expired. The power down location update means that the mobile station performs location update before being powered off.
In other words, if the mobile station moves from one paging group to another paging group, it transmits a ranging request (RNG-REQ) message to a target base station so as to perform location update. The target base station having received the RNG-REQ message transmits a ranging response (RNG-RSP) message to the mobile station. In this case, the target base station includes a paging group identifier (PG_ID) in the RNG-RSP message. In addition, the target base station informs a paging controller of a new location of the mobile station.
Recently, various technologies for a femtocell BS have been defined and introduced to cover an indoor space or a shadow area not covered by a macrocell BS. The femtocell is a low-power mini cell area managed by an indoor BS, designed for use in residential and/or small business environments. While the femtocell is used inter-changeably with the term ‘picocell’, the femtocell is regarded as a more advanced type form of the picocell. The femtocell BS is a small cellular BS that connects to a broadband router. The femtocell BS functions to connect legacy 2nd Generation (2G) and/or 3rd Generation (3G) voice and data to a backbone network of a mobile communication service provider via a Digital Subscriber Line (DSL) link or the like.
A femtocell base station (BS) may cover an indoor space or a shadow area not covered by the macrocell BS and may support a high data transmission rate. The femtocell BS may be installed in an overlay form within a macrocell or in a non-overlay form in an area uncovered by the macrocell BS.
The femtocell BS is classified into two types: a Closed Subscriber Group (CSG) femtocell BS and an Open Subscriber Group (OSG) femtocell BS. The CSG femtocell BS groups MSs which can access the CSG femtocell BS and assigns a CSG IDentification (ID) to the groped MSs. Only the MSs to which the CSG ID is assigned can access the femtocell BS. The OSG femtocell BS refers to a BS that all MSs can access.
The operation mode of the CSG BS is classified into an open access mode, a closed access mode, and a hybrid access mode.
The femtocell BS in the open access mode can access all users (i.e., all MSs), such that the MS does not compare a CSG ID received from the femtocell BS with a user CSG list of the MS and immediately performs initial entry into the femtocell BS. The user CSG list is a CSG ID list of a femtocell to which the MS may connect, and the MS can manage the user CSG list (or the CSG ID list).
If the femtocell BS is in the closed access mode, only a specific user (or a specific MS) can access the femtocell BS, the MS compares a CSG ID received from the femtocell BS with a user CSG list of the MS, such that it can perform initial entry into the femtocell BS only when the received CSG ID is present in the user CSG list of the MS. The hybrid access mode can be operated in one or both of the open access mode and the closed access mode.
The above-mentioned femtocell has the following advantages.
Recently, a new research paper has proposed a method for the femtocell to expedite the spread of 3G technology and greatly increase indoor coverage. Up to 2012, it is expected that the number of the femtocell BS users throughout the world will increase to about one hundred and two million, and the number of access points (APs) serving as BSs will also increase to about sixty-two million. The femtocell can strengthen the cell coverage and increase the quality of a voice service. Also, mobile communication service providers may provide subscribers with a variety of data services through femtocells, such that the subscribers can be easily accustomed to the 3G technology.
In other words, the communication system based on the femtocell may improve cell coverage, facilitate infrastructure installation with lower cost as compared to a general BS, and accelerate Fixed Mobile Convergence (FMC).
One or more femtocell BSs are grouped according to specific services or groups so as to constitute a femtocell group. For example, a femtocell group that can access only a specific MS may be referred to as a Closed Subscriber Group (CSG). A femtocell BS (FBS) recognizes a CSG ID of the MS so that it allows access of only the MS subscribed to the CSG.
FIG. 2 shows an example of a femtocell arrangement structure for use in an overlay network.
Referring to FIG. 2, a backbone network of the femtocell BS is directly connected to an Internet Service Provider (ISP) network connected by wire, and a Femtocell GateWay (FGW) may be located at an access point between the backbone network and the ISP network. The FGW may be used as an access point for communication with a Macrocell (or Macro) Base Station (MBS).
The FGW may be directly connected to femtocell BSs, or may be located between a core network and an ISP network so as to be an integrated server for each ISP. In addition, the system may guarantee its communication with a macrocell (or macro) BS (MBS) through a CNS GW or an ASN GW irrespective of the location of the FGW. In the overlay network, the MBS may transmit/receive or store some or all information units for FBSs.
If femtocell BS configuration is completed, the MBS may recognize other information including FBS location information. Therefore, the MBS may directly communicate with the FBS through an air interface.
In this case, the macro BS including a Home Femto BS of an MS and a Closed Subscriber Group (CSG) femto BS may be referred to as an Overlay Macro BS.
FIG. 3 shows an example of a femtocell arrangement structure in a non-overlay network.
If many users are temporarily crowded at a boundary among MBSs in a non-overlay structure, FBSs may be installed at a boundary among macrocells. In this case, the MBS may not store all information of FBSs therein. At this time, the FGW may serve as an access point where the FGW can communicate with the MBS in the same manner as in the overlay structure.
The femtocell BS has small coverage. Thus, if location update is performed whenever the femtocell BS moves out of the femtocell area, the number of location updates is excessively increased.